This invention relates to digital photography, and more particularly to verification of image authenticity.
Digital photography enables users to take photographs without conventional chemically-based film, providing a number of advantages. A solid state image detector, such as a charge coupled device (CCD), records images which are stored electronically. Other devices such as scanners are also used to generate digital images.
Once a digital image is created by a camera or any other means, it becomes a data file that is essentially a string of binary bits. Other than the stored visual content of the image, the data contains no information about the image""s physical source or time and location of origin. Like other types of computer files, an image data file may have appended to supplementary meta-data it that describe its origin. For example, the computer file itself may identify the time and date of the file""s creation. However, both the image data and the meta-data are easily altered, with no means subsequently to establish whether there has been any alteration, even with a close examination of the data or image stored in the data.
Conventional film photographs may be physically examined by discerning experts to detect image alterations, as alterations to the physical film, paper and/or grain patterns can be identified. However, chemically-based film photographs do not necessarily document the sources, times and locations of their creation.
The ease and undetectability of the modification of digital images makes them inferior to film images for any purpose such as legal documentation or law enforcement where the integrity of the image is paramount. Moreover, the lack of positive, unalterable supplementary information associated with an image limits the utility of even conventional film photographs for certain critical evidentiary purposes.
The present invention overcomes the limitations of the prior art by providing a method and apparatus for authenticating a digital file. The method and apparatus operate by generating an image file or other data file in a first device such as a camera. The file is processed using a function to generate a second data file, which is stored in the device. It is then determined if a suspect data file is identical to the image file by processing the suspect data file with the same function, and comparing the result with the second data file. The second data files for a multitude of images may be permanently stored in the device, and the function used to generate the second data file operates to ensure that the second data file is much smaller than the image data file.